Powder feed mechanism employing vibrating screen



Aug. 1, 1967 w. PROSKAUER 3 POWDER FEED MECHANISM EMPLOYING VIBRATING SCREEN Filed Feb. 5, l964 5s TRANSDUCER DRIVER 66 1; o o o INVENTOR. I

A 7TORNEX United States Patent 3,333,537 POWDER FEED MECHANISM EMPLOYING VIBRATING SCREEN Walter Proskauer, San Francisco, Calif., assignor to Electrostatic Printing Corporation of America, San Francisco, Califi, a corporation of California Filed Feb. 3, 1964, Ser. No. 341,853 6 Claims. (Cl. 101364) This invention relates to electrostatic printing systems of the type which employ an electric field for transferring electroscopic powder particles to a receiving substrate to form an image thereon, and more particularly to an improvement in the powder feed mechanism.

In a Patent No. 3,081,698 to Childress et a1. there is described and claimed an electrostatic printing system wherein powder particles having electroscopic properties are fed through openings in an image forming electrode into an electric field. The openings are arranged in a pattern desired to be printed. The electric field carries the powder to a substrate where it is deposited, forming thereon the same image as that of the openings in the image forming electrode. The substrate is then moved to a location at which the image can be permanently fixed thereto. One of the presently used techniques employed for urging the powder particles through the openings in the image forming electrode is to use a rotating brush which rubs against the rear surface of the image electrode imparting sufiicient energy to the powder particles to cause them to move through the openings of the image electrode into the electric field. Since powder is transmitted through the image openings only in places where the brush fibers contact the image electrode, in the case of a roller brush this means that the brush itself must both rotate and traverse the length of the image electrode to, at one time or another, contact all points on the powderj image forming electrode. Where the powder image forming electrode has a substantial size, the time required by the 'brush for covering the entire electrode area for urging the powder particles through the powder image forming electrode may be substantial, especially when compared to the time required for transferring the powder particles which is on the order of a millisecond.

An object of this invention is to provide an arrangement for urging powder particles through all areas of an image forming electrode substantially simultaneously. Another object of this invention is to increase the speed of the powder particle feeding arrangement in an electrostatic printing system of the type described.

Yet another object of the present invention is the provision of a novel and improved powder particle feeding arrangement in an electrostatic printing system of the type described.

These and other objects of the present invention may be achieved by providing a plurality of parallel, stretched elongated, resilient members which are held adjacent to that side of the powder image forming member in an electrostatic printing system from which electroscopic powder particles are urged through openings into the electric field. The elongated members have powder particles deposited thereover. They are then vibrated whereby they impart sufiicient energy to the powder particles to enable them to pass through the openings in the image forming member into the electric field. The stretched elongated members which will herein be designated as a loading screen are preferably placed near the bottom of a powder container, the bottom side of which opens onto an image forming screen electrode. In this manner, the powder loading screen is always loaded with powder and can cause a powder charge to pass through the image electrode apertures as frequently as is required for the purpose of successive printings.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well'as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective exploded view of an arrangement of the powder feed mechanism in accordance with this invention.

FIGURE 2 is a perspective view illustrating an arrangement for the embodiment of the invention.

FIGURE 3 schematically shows another mechanism for vibrating the wires of the powder loading screen in accordance with this invention; and

FIGURE 4 illustrates schematically how the powder loading screen can be biased in order to assist in the control of the density of powder feed.

Referring now to FIG. 1, there is seen a perspective view of an arrangement of an electrostatic printing system, including an image forming screen electrode 10,

having openings 12 therethrough arranged in the image pattern desired to be printed. A substrate 14 which may be paper, is interposed between the image forming electrode 10 and a conductive backplate 16. An electric field is established between the image electrode 10 and the conductive backplate 16 by means of a source of potential 18 connected between these two electrodes. Powder particles having electroscopic properties are urged through the openings 12 into the electric field established between the electrodes 10 and 16. The electric field carries the powder particles in the pattern provided by the openings to the substrate 14 to which they adhere until they can be subsequently fixed.

As previously indicated, the previous arrangement for transferring the powder particles through the openings 12 is to use a rotating brush which literally rubs these powder particles through these openings. In accordance with this invention, there is provided a powder feeding screen 20 which may consist of a frame 22 for holding a plurality of elongated members such as wires 24 under tension. The screen is held close to the loading side of the image electrode 10. The wires 24 of the screen are then loaded with powder in any suitable manas for example, by the simple method of covering the wires by pouring the powder thereon from a container. The wires are then plucked or vibrated by any suitable expedient, some of which will be shown subsequently herein. The vibrating wires urge the powder particles downwardthrough the openings in the image electrode 10 and into the electric field.

There are a number of advantages to the loading mechanism just described. The most obvious one is that the entire image areais loaded substantially simultaneously and thus the electrostatic printing process can be made .to takeplace in a'much shorter time than was required when a brush had to be rotated over the entire screen area. Since an entire area can be printed simultaneously with the arrangement shown and described, the area size itself may be increased without increasing the required printing time, as was the case heretofore. Furthermore, brushes of the type used heretofore do wear out with use, whereas the wires of the powder loading screen do not wear out with use. A control over the amount of powder being urged through the image apertures and thereby the density of printing can be readily made with the powder loading screen by controlling the amplitude of vibration of the wires. This can be done by suitable tension varying means or by controlling the frequency and amplitude of the plucking action applied to the wires of the powder loading screen to cause them to vibrate. Obviously no such control is afforded by the brush method of loading powder.

FIGURE 2 is an isomeric view of an arrangement for loading powder in accordance with this invention. A powder particle container 30 has a powder loading screen 32 placed substantially close to the bottom thereof. The wires of the powder loading screen extend outside of the powder container to a support bar 34. A transducer driver 36 causes a transducer bar 38 to vibrate and to rub against the wires of the loading screen 32 causing them to vibrate. The transducer 38 may be any of the well known types such as a magnetostrictive transducer or a piezoelectric transducer to which driving energy is applied by the transducer driver 36. Alternatively, the transducer 38 may be a bar which is vibrated by a solenoid coil contained in the transducer driver 36. The transducer bar 38 is in actual physical contact with the wires of the powder loading screen and is driven preferably at a frequency which is greater than that at which the wires of the powder loading screen vibrate. By controlling the amplitude and/or frequency of the vibration of the transducer 38, the amplitude and frequency of the wires of the screen 32 are controlled whereby the density of the powder image finally resulting is controlled.-

The bottom of the container 30 is positioned over a powder image forming screen 40. Spaced therefrom is the image substrate 42 and spaced therefrom is the conductive backplate 44.

Referring now to FIGURE 3, there may be seen another arrangement, shown in schematic form, for vibrating the wires of the image loading screen. This arrangement comprises a closed loop belt 46 which is stretched between and rotatably driven by two spaced rollers 48, 50. The belt carries the wire plucking members 52 which, as the belt is driven past the wires of the powder loading screen 54, pluck these wires causing them to vibrate and thus load powder through the openings in an image electrode 56 The substrate 58 receives the powder through these openings as a result of the electric field established between the image forming screen 56 and the conductive backplate 60. The potential source 62 establishes the electric field.

A further control over the density of the powder image is afforded by applying a biasing voltage to the wires of the powder image loading screen. As shown schematically in FIGURE 4, a variable potential source 64 is connected between the wires of the powder image loading screen 66 and the powder image forming electrode 68. All the wires of the screen 66 may be connected to the potential source 64 by making one ofthe sides of the frame, for example 34, conductive whereby connecting the potential source thereto applies said potential to all of the wires of the powder image loading screen. A second potential source 70 is connected between the powder image forming screen 68 and the backplate 72. The substrate 74 is positioned therebetween, as was explained previously.

By vibrating the wires of the screen 66 in one of the ways previously described and by controlling the amplitude of the voltage applied to the powder loading screen 66 and the powder image forming screen 68, the density of the powder image which is deposited on the substrate 74 may be controlled very, very closely. It is also possible to omit the connection between the potential sources 64 and 70 to the screen 68 and just permit a potential to exist between the powder image loading screen 66 and the backplate 72. However, the arrangement shown in FIGURE 4 is the preferred one.

While the elongated members of the powder image loading screen have been referred to as wires, it should be understood that, except where these are required to be "conductive for the purpose of affording further control of powder image density, other materials than metal may be employed. These materials may range just as do the strings of musical instruments from gut and nylon through wire wound nylon to wire strings.

There has accordingly been shown and described herein a novel, useful and simple arrangement for affording a simultaneous transfer of powder through a powder image forming electrode in an electrostatic printing system.

What is claimed is:

1. In an electrostatic printing system having a source of electroscopic powder particles, a powder image forming member, an image receiving substrate, means for establishing an electric field between said powder image forming member and said image receiving substrate, and means for applying powder particles from said source to said powder image forming member to be carried in the shape of said image to said receiving substrate, the improvement in apparatus for feeding powder to said powder image forming member comprising a powder loading screen placed adjacent to the side of said powder image forming member to which powder particles are applied to be urged therethrough, said powder loading screen comprising a plurality of elongated resilient members, means for supporting said plurality of elongated resilient members solely by their ends to be substantially parallel with one another and to be individually vibratable, means for applying powder from said source to said powder loading screen, and means for applying vibrating energy to the plurality of elongated resilient members of said powder loading screen for individually vibrating them while their ends remain substantially stationary for urging powder particles through said powder loading screen and through said powder image forming member.

2. In an electrostatic printing system having an image forming electrode with apertures therethrough in the form of a desired image, a backing electrode spaced from said image forming electrode, means for establishing an electric field between said image forming electrode and said backing electrode, an image receiving substrate positioned between said image forming electrode and said backing electrode, a source of electroscopic power particles, and means for urging electroscopic powder particles from said source through the apertures of said image forming electrode to be carried by said electric field to said substrate, the improvement in apparatus for urging said powder particles through said apertures in said image forming electrode comprising a plurality of elongated resilient members, frame means for holding said elongated resilient members solely by their opposite ends positioned substantially parallel to one another and to be individually vibratable, means positioning said elongated resilient members adjacent the surface of said image forming member, means for applying powder particles to the elongated resilient members from said source, and means for applying vibrating energy to said elongated resilient members for individually vibrating them while their ends remain substantially stationary to urge powder particles through the apertures in said image forming electrode.

3. Apparatus as recited in claim 2 wherein said means for applying vibrating energy to said elongated resilient members comprise an electromagnetic transducer positioned to contact said elongated resilient members, and means for exciting said electromagnetic transducer.

4. Apparatus as recited in claim 2 wherein said means for applying vibrating energy to said elongated resilient members comprises a plurality of plucking fingers, a belt v posite said image forming electrode, a substrate positioned between said image electrode and said backing electrode, means for establishing an electric field between said image electrode and said backing electrode, a source of electroscopic powder particles, and means for applying powder particles from said source to said image forming electrode to pass therethrough and be carried by said electric field in the shape of said desired image to said substrate, the improvement in apparatus for applying powder particles from said source through said apertures in said image forming electrode comprising a plurality of elongated resilient members, frame means for holding said elongated resilient members solely by their opposite ends positioned substantially parallel to one another to be individually vibratable, means positioning said frame means to hold said elongated resilient members adjacent the surface of said image forming member through which powder particles are urged, means for applying powder particles from said source to said elongated resilient members, means for applying vibrating energy to said elongated resilient members to cause them to vibrate while their ends remain substantially stationary, and means for establishing a potential between said elongated resilient members and said image forming electrode for assisting in controlling powder feed density,

6. In an electrostatic printing system having an image forming electrode with apertures therethrough in the form of a desired image, a backing electrode spaced opposite to said image forming electrode, .a substrate positioned between said backing electrode and image forming electrode, means for establishing an electric field between said image forming electrode and said backing electrode, a source of electroscopic powder particles, and means for applying electroscopic powder particles to the apertures in said image forming electrode to pass therethrough to be carried by the electric field in the form of said image to said substrate, the improvement in apparatus for urging said powder particles through said apertures in said image forming electrode comprising a container for said source of powder particles, said container having an open bottom, a plurality of elongated resilient individually vibratable members, means supporting said plurality of elongated resilient members solely by their ends substantially parallel to one another across said open bottom of said container, said container being positioned to place said resilient members adjacent said image forming electrade, and means for applying vibratory energy to said elongated resilient members to cause them to individually vibrate while their ends remain stationary to urge powder particles through the apertures of said image forming electrode.

References Cited UNITED STATES PATENTS 814,952 3/1906 Pitts 209-254 821,502 5/1906 Kelficr 209-254 2,173,032 9/1939 Wintermute 117-17 2,579,514 12/1951 Rhodes 107-7.1 2,675,330 4/1954 Schwartz et al. 117-17 2,907,404 10/1959 Mare 209-400 X 3,039,696 6/1962 Point et al. 118-627 3,081,698 3/1963 Childress et al. 101-129 3,123,558 3/1964 Sullivan 209-393 X 3,134,849 5/1964 Frohbach et al. 3,180,256 4/1965 Kramer et a1 101-125 X ROBERT E, PULFREY, Primary Examiner; E. S. BURR, P. WOODS, Assistant Examiners, 

1. IN AN ELECTROSTATIC PRINTING SYSTEM HAVING A SOURCE OF ELECTROSCOPIC POWDER PARTICLES, A POWDER IMAGE FORMING MEMBER, AN IMAGE RECEIVING SUBSTRATE MEANS FOR ESTABLISHING AN ELECTRIC FIELD BETWEEN SAID POWDER IMAGE FORMING MEMBER AND SAID IMAGE RECEIVING SUBSTRATE, AND MEANS FOR APPLYING POWDER PARTICLES FROM SAID SOURCE TO SAID POWDER IMAGE FORMING MEMBER TO BE CARRIED IN THE SHAPE OF SAID IMAGE TO SAID RECEIVING SUBSTRATE, THE IMPROVEMENT IN APPARATUS FOR FEEDING POWDER TO SAID POWDER IMAGE FORMING MEMBER COMPRISING A POWDER LOADING SCREEN PLACED ADJACENT TO THE SIDE OF SAID POWDER IMAGE FORMING MEMBER TO WHICH POWDER PARTICLES ARE APPLIED TO BE URGED THERETHROUGH, SAID POWDER LOADING SCREEN COMPRISING A PLURALITY OF ELONGATED RESILIENT MEMBERS, MEANS FOR SUPPORTING SAID PLURALITY OF ELONGATED RESILIENT MEMBERS SOLELY BY THEIR ENDS TO BE SUBSTATIALLY PARALLEL WITH ONE ANOTHER AND TO BE INDIVIDUALLY VIBRATABLE, MEANS FOR APPLYING POWDER FROM SAID SOURCE TO SAID POWDER LOADING SCREEN, AND MEANS FOR APPLYING VIBRATING THEM WHILE THEIR PLURALITY OF ELONGATED RESILIENT MEMBERS OF SAID POWDER LOADING SCREEN FOR INDIVIDUALLY VIBRATING THEM WHILE THEIR ENDS REMAIN SUBSTANTIALLY STATIONARY FOR URGING POWDER PARTICLES THROUGH SAID POWER LOADING SCREEN AND THROUGH SAID POWDER IMAGE FORMING MEMBER. 